The U.S. Army Corps of Engineers and others involved in hydropower generation are actively developing techniques to move juvenile salmon past their facilities without entraining them through turbines (see, e.g., Northwest Power Planning Council, Columbia River Basin Fish and Wildlife Program, Portland, Oreg., 1994; National Marine Fisheries Service, "Biological opinion: reinitiation of consultation on 1994-1998 operation of the federal Columbia River power system and juvenile transportation program in 1995 and future years." 1995). Constructing fish bypasses around hydroelectric projects can cost millions of dollars, and yet the bypasses may not work as well as their designers had hoped. To develop methods for improving the survival of fish near hydroelectric projects, it is important to evaluate the behavior of the fish as they approach and pass through a hydroelectric project. In studying the behavior of fish near hydroelectric projects, it is desirable to be able to track the position of individual fish on a fine scale, and in noisy environments, and to distinguish one species of fish from another.
Conventional methods of tracking underwater objects are useful in many instances but suffer from various limitations. For example, conventional fixed location hydroacoustics is typically unable to track individual fish, weak in species discrimination, and can be ineffective in noisy environments. On the other hand, conventional radio telemetry provides species-specific tracking capabilities, but is generally inadequate when location accuracy is required, especially in deep water such as in the forebay or reservoir of a hydroelectric power system. Thus, despite prior efforts, there remains a need for a method that provides accurate positional tracking of underwater objects, especially particular fish species, in noisy environments such as the forebay of hydroelectric projects.